AM stereo systems have been proposed that transmit an infrasonic pilot signal such as 5 Hz. which when detected closes an electronic stereo switch which permits demodulation of the composite stereo signal and also causes a stereo indicator lamp to be energized. Prior art pilot signal detectors use a low Q bandpass filter or a low pass filter with output voltage detection. These approaches suffer from a high occurrence of false triggering. False triggering can occur when the carrier of two AM stations are separated by the frequency of the pilot signal. FCC Rules allow the carriers to be as much as 20 Hz. off the assigned frequency. Thus, there is a high probability of low frequency beat note near 5 Hz. being present. False triggering can also be caused by AM to PM conversion to the receiver or from power line interference. The problem of false triggering can be alleviated to some degree by using a high Q bandpass filter but this approach has the tendency to ring when a transient near the pilot frequency occurs.